Help me find a 4-gang, 50k pot? - diyAudio
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Old 13th March 2010, 06:34 AM   #1
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Default Help me find a 4-gang, 50k pot?

Hi all,

I need to replace a pot in a subwoofer preamp. It controls the freq of 2 2nd order Sallen-Key filters (or LR4), thus the 4 resistor elements. The circuit works fine if I insert discrete resistors although 3 of the end-to-end resistances are 3MR or more - so it's amazingly a failure of 3/4 of the resistive elements!

Please see the pics of the pot I removed from the preamp. I would describe it as: 4 gang, horizontal PCB mount, C taper, 50k, no click/detent, 12.5mm above PCB with 20mm long, 6mm knurled length, 18 teeth shaft.

I contacted the manufacturer of the sub amp, and they didn't design it and don't support it. The pot is marked with "HV" on the pot bodies, but I don't know if that's the manufacturer or something else. So no luck there.

I then looked at Mouser, Digikey, and other places in the US without any luck. Googling didn't turn up any parts. Can anyone suggest someplace (preferably in the US) that might carry this pot?

I found the part I need at Taiwan Alpha (part number: RV124F-21_-20K-C50K-_0) and Alpha Products (part number: Alpha Products 3RP/1240G 2 A B C 50K 0), but neither one had the part available and would require a 1000 piece order to make any. Although I will say that the Taiwan Alpha folks were exceptionally generous and courteous to me. I also found a few Asian suppliers with seemingly compatible parts, but I didn't contact them because I'm not feeling like it would be worthwhile.

Any suggestions of how to get a replacement pot would be wonderful. TIA!
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Old 13th March 2010, 07:04 AM   #2
poynton is offline poynton  United Kingdom
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Probably the "easiest" fix would be to buy a few dual gang pots of similar size and type.

Dismantle them and rebuild your original.

I've done this before - quite easy and straightforward if a little fiddly.


Andy


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Old 14th March 2010, 05:28 PM   #3
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I've read that a 100k resistor across pin 1 and 3 of a 100k linear pot will make a 50k reverse log.

I'll amdit I don't have the math skills to cofirm that though.

Last edited by theAnonymous1; 14th March 2010 at 05:39 PM.
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Old 14th March 2010, 05:38 PM   #4
Pars is offline Pars  United States
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Ebay seller familygate has lots of Alps pots. Here is a 4-gang log 10K or 50K pot, but its motorized:
eBay.ie: ALPS Quad Potentiometer RK27114MC motorized pot 10K 50K (item 250467804650 end time 16-Mar-10 07:46:33 GMT)
They do have a non-motorized version, but I only found 5K or 10K (but did not look exhaustively).
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Old 14th March 2010, 06:10 PM   #5
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Quote:
Originally Posted by theAnonymous1 View Post
I've read that a 100k resistor across pin 1 and 3 of a 100k linear pot will make a 50k reverse log.

I'll amdit I don't have the math skills to cofirm that though.
OK, I guess I read wrong.

After more searching and reading, it looks like you can take a linear taper pot of 5x the value you need, and the put a resistor of 1.25x your desired RevLog taper across pin 2 and 3.

50k x 5 = B250k
50k x 1.25 = 62.5k

So for C50k, you put a 62.5k resistor across pin 2 and 3 of a B250k.
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Old 14th March 2010, 08:17 PM   #6
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I find that getting in touch with manufacturers can be a big help. If you are polite and explain what you want, some are very willing to help. Some even go out of there way to help.
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Old 14th March 2010, 10:07 PM   #7
gootee is offline gootee  United States
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I did a search at google.com for

quad concentric pot OR potentiometer

and found this PDF about a family of modular pots and switches that can be configured however you want (up to four sections concentrically):

http://www.potentiometers.com/pdf/catalog70.pdf .

And the link below has new and used parts for Tektronix and HP/Agilent test equipment, which includes lots of interesting pot configurations (and lots of other cool parts!). Maybe it'll give you some information about who makes what.

Tektronix Electronic Test Equipment Parts - Pots, Resistor Networks

Cheers,

Tom Gootee
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Old 14th March 2010, 11:11 PM   #8
gootee is offline gootee  United States
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Do a search at google.com for:

multi-gang pot OR potentiometer

Note that the "OR" must be in upper case (caps).

Also, you might want to check out the Vishay / Sfernice P9A series. They can have up to seven modules on a shaft. Mouser.com has the dual 50K (but not sure if they carry other than linear taper). You could probably buy two of them and make them into a quad. Go to mouser and search for 72-p9a. You can see an older mouser catalog page with them, here: http://www.mouser.com/catalog/629/544.PDF . (Looks like the price on the dual 50k linear ones has about doubled since then.)

Last edited by gootee; 14th March 2010 at 11:21 PM.
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Old 17th March 2010, 05:08 AM   #9
Garyepe is offline Garyepe  China
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please check this photos, Does it same as your need ?

You can add my MSN garyhjj456@hotmail.com


Gary
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Old 17th March 2010, 07:32 AM   #10
Garyepe is offline Garyepe  China
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Default specs

You can check the specs of it.

Gary
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